1. Field of the Invention
The invention relates to a method of controlling the temperature of an injection mold during each molding cycles of recurring molding cycles. A single molding cycle consists of pressure feeding molding material into the mold recess or the mold recesses of an injection mold, curing the material therein, and removing the molded material from the mold.
Applicant's method controls the temperature of the injection mold by comparing a present nominal temperature to an actual measured temperature, said actual temperature being measured by at least one temperature sensor. An amount of a cooling and heating medium is intermittently supplied to each molding cycle depending on the deviation of the measured actual temperature from the desired nominal temperature of the molding cycle. The comparison of the actual temperature and the nominal temperature is performed during each cycle at at least one point of time for each single molding cycle period. The method of controlling the temperature is suitable for use with plastic and aluminum die casting.
2. Background Art
A known method is shown in U.S. Pat. No. 4,420,446 or U.S. Pat. No. 4,354,812. In these known methods, the temperature of the injection mold is continuously sensed by means of a probe, and compared with a nominal value and, depending on whether the measured temperature exceeds or falls short of the desired nominal temperature, cooling fluid, in particular cooling water, is supplied through cooling channels or switched off. This method works without specifically taking into account the temperature distribution and the need of a cooling medium in the respective mold, these values varying extremely from case to case depending on the geometry and size of the mold. Consequently, optimal temperature distribution cannot be achieved with the known method. But optimal temperature control is needed to ensure a method which provides quality of the final product on the one hand, and achieves optimally short cycle times on the other hand. Cycle times must be adequately long enough to ensure sufficient curing of the molten material in the mold prior to ejection, but short enough to avoid excessive dwell times of the molded part of the mold. Temperature control must also be taken into account. Temperature control must ensure that even the most remote end of the mold recess, even for rather long mold channels, be reached by the still fluid injection-molding compound so that no cavities remain. On the other hand, the temperature control must be precise enough to avoid over heating the mold so as to require more of a cooling medium than necessary to be supplied for cooling and curing the molded part and thus increasing the amount of cooling time that has to pass.